The present invention relates to an erasable writing medium or ink that can be dispensed through a porous tip or ballpoint writing instrument that can be removed with comparative ease with a substantially non-abrasive eraser, such as a common pencil eraser.
In producing written images and characters with writing instruments, obtaining a high degree of indelibility is not necessarily desirable. For example, a person may want a writing medium which is easily removable by mechanical means from the writing surface, i.e., an erasable writing medium. If truly erasable, the writing medium must be capable of being removed from the writing surface to which it has been applied without significant damage, such as abrasion, to the writing surface. Since the most commonly used writing surface is paper, a general discussion of the characteristics and composition of paper is helpful for an understanding of the present invention.
Paper is essentially a mat of randomly distributed cellulose fibers. Because of the random orientation, the paper surface contains numerous voids which exist between the randomly oriented cellulose fibers. Therefore, for a writing medium to be truly erasable, at least that portion of the writing medium that contains the colorant portion of the medium must be prevented from penetrating to any substantial degree into those voids. Otherwise, removal of the colorant by erasing could not be accomplished without some damage in the form of abrasion to the writing surface. Therefore, a need exists for a writing medium that is not absorbed by the writing surface, namely paper, but which writing medium contains a water soluble colorant or dye and can be used in ballpoint and porous tip pens. The writing medium should also resist drying on the tip of the pen but dry relatively rapidly when applied to a writing surface.